Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $71.34   7.354%   $76.5863   $76.59   $76.60   $76.60  
  Purchase #2 $34.26   4.245%   $35.7143   $35.71   $35.70   $35.70  
  Purchase #3 $155.79   7.291%   $167.1486   $167.15   $167.15   $167.10  
  Purchase #4 $245.92   9.765%   $269.9341   $269.93   $269.95   $269.90  
  Purchase #5 $123.41   13.283%   $139.8026   $139.80   $139.80   $139.80  
  Purchase #6 $131.31   11.748%   $146.7363   $146.74   $146.75   $146.70  
  Purchase #7 $49.55   6.213%   $52.6285   $52.63   $52.65   $52.60  
  7 purchase totals = $811.58       $888.5507   $888.55   $888.60   $888.40